Fuel cells have the potential to become an economically viable means of converting chemical energy into electrical energy. For example, in a polymer-electrolyte membrane (PEM) fuel cell, also known as a proton exchange membrane fuel cell, hydrogen and oxygen are combined for the production of electrical energy. Air is the customary source of oxygen while the oxidant can be any hydrogen fuel stock including hydrogen, methane, natural gas and ethanol. Other than pure hydrogen, the fuel source may require a local refining process to produce the hydrogen in a form acceptable to the PEM membranes. This refining is accomplished in a reformer. The energy conversion in the fuel cell occurs through oxidation, which requires pressurization of both the oxidant and the oxidizing agent. The reforming system consumes approximately one-quarter of the air requirement of the overall power system to produce the high pressure required by the air system.
Electrical power systems utilizing fuel cells are comprised of several subsystems requiring the compression of air and/or other gases in order to operate. Each of these subsystems operates best under distinctly different pressure profiles. The most common approach to obtain all of the necessary pressures is to utilize a complete gaseous supply system including a compressor, a drive motor, a motor controller and perhaps an expander for each subsystem. This approach creates a large parasitic electrical power draw on the overall power system and therefore represents a significant increase in expense, size and inefficiency of the power system.
Hydrogen peroxide (H2O2) has been used for many decades as a source of oxygen for the combustion of hydrocarbon fuels and for generating steam and other gases used to propel rockets. Additionally, it was successfully used as an oxygen source in submarines as early as the 1930s. Hydrogen peroxide, available as a relatively safe fluid represents a hydrogen and oxygen-rich source of fuel for a fuel cell power system if an efficient means of separating and delivering these molecular components to the fuel cell stack can be produced. Thus, there is a need for a simpler, less costly hydrogen and oxygen supply system for a fuel cell based on hydrogen peroxide that reduces or eliminates the need for an air compressing system to support reforming needs. Preferably the system would also eliminate the cost of the expander and downsize any air system drive motor requirements.
Oxygen has been traditionally provided in the form of an air stream to the cathode side of the fuel cell stack. In all cases, there is a motive device such as a fan, blower or compressor to move the oxygen bearing air through the fuel cell stack. The power density of the stack has a direct relationship with the concentration of oxygen and hydrogen at the fuel cell membrane electrode assembly (MEA). Assuming that the production of electrical power is not limited by the hydrogen concentration on the anode side of the MEA, when the air stream is pressurized, the stack MEA can produce significantly more electrical current proportional to the density of oxygen near the membrane. Thus, the current approach to increasing the power output of fuel cells is to increase the motive power provided to the mechanical device used to move air through the fuel cell stack thereby increasing the density of the air stream. Though the total power output from the fuel cell will increase, the percentage of motive power provided to the air-moving device continually increases at a faster rate thereby reducing the overall efficiency of the system. Thus, there is a need for a method of reducing the percentage of the parasitic load to the electrical output of a fuel cell represented by these mechanical devices.